1. Field of the Invention
The present invention relates to a thin-film magnetic head for magnetic recording equipped an electromagnetic coil element with a coil layer and a coil-insulating layer, a head gimbal assembly (HGA) with the thin-film magnetic head, and a magnetic disk drive apparatus with the HGA.
2. Description of the Related Art
A thin-film magnetic head which a magnetic disk drive apparatus comprises flies with a predetermined spacing (flying height) above a rotating magnetic disk which is a magnetic recording medium, in writing or reading signals. The thin-film magnetic head, on flying state, writes data to the magnetic disk using write magnetic field generating from an electromagnetic coil element, and reads data with sensing a signal field from the magnetic disk using a magnetoresistive (MR) effect element.
With higher recording density due to increasing data storage capacity in recent years, a track width of the thin-film magnetic head is becoming smaller. In order to avoid a degradation of writing and reading performance due to the smaller track width, an effective magnetic distance dM is becoming smaller, which is a distance between an edge of the magnetic head element composed of the electromagnetic coil element and the MR effect element, and a surface of the magnetic disk. The magnetic distance dM is actually reduced down to approximately 10 nm or less.
In case of applying write currents to the electromagnetic coil element in the magnetic head element, a temperature of the magnetic head element increases by Joule heat, eddy current loss heat, and so on. Also, by heat from other parts in the magnetic disk drive apparatus, the temperature of the magnetic head element may also increase with a temperature rise of inside of the magnetic disk drive apparatus according to an external use environment.
With a rise of “an environment temperature” that is a temperature without actively controlling by a heat from inside or outside of the magnetic head element, a so-called thermal pole tip protrusion (TPTP) phenomenon, that an end of the magnetic head element protrudes to a magnetic disk surface direction, occurs. Actually, in the magnetic head element, a write coil layer formed of a conductive metal material such as Cu, a magnetic pole layer formed of a magnetic metal material, and a write coil-insulating layer formed of a plastic material such as photo-resist hold the most of its volume, whereas, a whole overcoat layer of the magnetic head element is formed of insulation material such as alumina (Al2O3). In this case, a heat expansion coefficient of the metal material and a heat expansion coefficient of plastic material are two to three times and ten times larger than that of the insulation material, respectively. As a result, the large TPTP phenomenon occurs by a large difference of heat expansion coefficient between the magnetic head element and the overcoat layer.
In the case where the effective distance dM is a minute value as described above, there is likely to contact the protruded end of the magnetic head element with the surface of the magnetic disk. This contact might cause a problem (thermal asperity) that abnormal signals occur with a change of an electrical resistance value of the MR effect element by a friction heat in this contact. Furthermore, a danger of crush raises up.
The art for avoiding these problems is described, which controls the effective distance dM by actively using the TPTP phenomenon with providing the heating element in the thin-film magnetic head (for example, U.S. Pat. No. 5,991,113). This art designs the effective distance dM in prospect of the protrusion by a mount of heat of the heating element beforehand, and adjusts the effective distance dM by the amount of current flow to the heating element in driving. However, in case of adjusting the effective distance dM by using the heating element in this way, it is necessary to lower a degree of the TPTP phenomenon as much as possible according to the environment temperature that has difficulty with control.
As a way of suppressing the TPTP phenomenon due to the environment temperature, for example, U.S. Pat. No. 6,836,389 describes the magnetic head having an expansion joint with low Young's modulus between a final layer which contains a converter and a substrate. In this head, the expansion joint absorbs an expansion transformation of the final layer and the substrate. Also, U.S. Pat. No. 7,110,219 describes the art which solves a head crush problem with suppressing protrusion of the overcoat layer by forming a heating block layer which is a lower thermal conductivity in the overcoat layer. Furthermore, Japanese patent Publication No. 2000-306213A insists that the magnetic head is obtained, which does not occur a transformation increasing the danger of crush by providing a higher Young's modulus layer on the side of a flying surface of an upper protecting layer or a lower protecting layer and a lower Young's modulus layer on its rear.
Furthermore, US patent Publication No. 2005/0219749A describes a decreasing the TPTP phenomenon by regulating a volume of the insulating layer surrounding the write coil layer to a predetermined value for a thickness of a protecting layer. That is to say, although the art described in U.S. Pat. No. 6,836,389, U.S. Pat. No. 7,110,219 and, Japanese patent Publication No. 2000-306213A, use a particular component which consists of a special material, US patent Publication No. 2005/0219749A takes relatively easy measure.
However, in the above-described arts, the problem that the suppression of the TPTP phenomenon with environment temperature is not sufficient has occurred in same cases.
For example, as the art described in U.S. Pat. No. 6,836,389, it needs to be equivalent the heat expansion coefficient of basecoat to that of the metal layer which the converter contains, then it has a restriction to select a material. Further, the measure for the expansion transformation of the basecoat or the overcoat by the heat from the converter is not sufficient. Also, in U.S. Pat. No. 7,110,219, although it is possible to suppress the protrusion of the overcoat layer by the existence of the heating block layer, it is difficult to suppress the protrusion of the magnetic head element.
Further, in Japanese patent Publication No. 2000-306213A, as ranges of the size of the each protecting layer and the Young's modulus are not disclosed at all, it is difficult surely to suppress the TPTP phenomenon. In fact, as the protrusion of TPTP phenomenon is the order of one nanometer (nm) to ten nanometers, it is necessary to regulate the size of the each protecting layer and the Young's modulus in order to control and suppress such a minute volume. Further, as the ranges of these values affects the value of the heat expansion coefficient of the each protecting layer, in the art which has not a specific regulation about the heat expansion coefficient, it becomes difficult surely to suppress the TPTP phenomenon.
Such situation is similar to the art described in US patent Publication No. 2005/0219749A. Surely, although this art, which does not use a new particular component, takes easy measure relative to the art described in Japanese patent Publication No. 2000-306213A, it only regulates the volume of the insulating layer surrounding the write coil layer, but it does not concretely disclose the possible range of the Young's modulus or the heat expansion coefficient of insulating layer. In fact, the only regulation of the volume of the insulating layer is not sufficient for surely suppressing the TPTP phenomenon.